The biosynthesis of hemoglobin may be divided into three separate processes, initiation, elongation and termination, each of which may be further subdivided into a number of steps. Our research involves, primarily, the elongation process and, specifically, the interconversion of aminoacyl-tRNA binding sites on the ribosome during this peptide chain elongation phase. These sites, termed the "acceptor" site and "donor" site, have not been defined with respect to the physics-chemical nature of the ribosome. The practical definition of these sites is that peptidyl-tRNA in the donor site may participate in peptide bond formation (elongation of the peptide chain) while a similar molecule in the acceptor site is inactive. An elongation factor, a partially purified protein fraction termed EF2, is necessary for the "movement" of peptidyl-tRNA from the acceptor to the donor site. A second elongation factor, EF1, is responsible for the binding of aminoacyl-tRNA to the now vacant acceptor site. Each of these steps of the elongation process appears to require the hydrolysis of GTP. Our approach to studying the details of the elongation process consists of several facets: the purification of "active" ribosomes "trapped" in one step of this process, the purification of the EF2 factor, the use of various GTP analogues , the use of various fluorescent probes covalently attached to ribosomal to ribosomal proteins, and the study of the phosphorylation of reticulocyte ribosomal proteins to gain insight on the mechanism of GTP hydrolysis as well as on a possible control mechanism of hemoglobin synthesis.